Helicobacter pylori, a gram negative, urease-producing, spiral bacterium has been associated with gastritis, gastric and duodenal ulcers, and gastric cancer in humans. Animal models are needed to study the epidemiology and pathogenesis of H. pylori disease. H. pylori has limited host range, and natural infections in animals have only been reported in nonhuman primates and cats. Nonhuman primates are also commonly infected with Gastrospirillum, another gastric spiral bacterium which infects humans but whose pathogenic potential has not been fully investigated. The objectives of the current studies were to 1) develop a specific and sensitive serologic assay for identification of anti-H. pylori antibodies in rhesus monkey serum, as results from previous work suggested that the commercially available human ELISA was not sufficiently sensitive in the rhesus monkey, 2) identify a population of animals negative for H. pylori and Gastrospirillum to be used for subsequent experimental infection protocols, and 3) identify the prevalence of H. pylori and Gastrospirillum in rhesus monkeys infected with simian immunodeficiency virus (SIV), as gastritis is commonly observed in these animals. An ELISA utilizing rhesus-origin H. pylori antigens and an anti-rhesus IgG conjugate was developed to detect anti-H. pylori antibodies in rhesus monkey serum. The test had a sensitivity of 93% and a specificity of 100%. Six Cesarean-section derived, nursery reared, SPF rhesus monkeys, 8-12 months of age were anesthetized for gastric endoscopy. Gastric juice was aspirated for pH measurement and gastric pinch biopsies were obtained from the cardia, body, and antrum for H. pylori culture, urease assay, PCR, and histology to include H&E and Warthin-Starry stains. Blood was collected for serology. All animals were seronegative for H. pylori. All animals had acidic gastric pH (mean=1.4), and all samples were negative for urease. H. pylori was not identified by culture, PCR, or histology in any animal. No animals had gastritis or Gastrospirillum on histology. Results suggested that Cesarean-derived, nursery reared, SPF rhesus monkeys were negative for H. pylori and Gastrospirillum and would provide an ideal study population for the conduct of subsequent experimental infection studies which will be initiated in the near future. Additionally, samples were collected at necropsy from 24 SIV+ rhesus monkeys. Samples will be processed as described above to identify the prevalence of H. pylori infection in this test population.